Gas compressor and method for controlling flow rate thereof

ABSTRACT

Provided is a gas compressor with a variable diffuser system capable of suppressing stall and surge. The gas compressor includes i) an impeller fixed to a rotation shaft and having a plurality of blades each including a wing surface and an edge surface on an outer circumferential surface thereof; ii) a shroud surrounding the wing surface; iii) a ring valve installed on a diffuser passage connected with an outlet of the impeller and moving in a direction parallel to the rotation shaft to open and close the diffuser passage; iv) a plurality of veins installed in a circumferential direction of the diffuser passage outside the ring valve in the diffuser passage; and v) an actuator coupled with the ring valve and the plurality of veins to sequentially control movement of the ring valve and rotational angles of the veins.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication Nos. 10-2009-0019013 and 10-2009-0019011 filed in the KoreanIntellectual Property Office on Mar. 5, 2009 and Mar. 5, 2009, theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a gas compressor, and moreparticularly, to a variable diffuser system installed on a diffuserpassage connected with an impeller outlet to prevent stall and surge,and a method for controlling a flow rate of the gas compressor using thesame.

(b) Description of the Related Art

In general, a gas compressor accelerates and compresses gas with acentrifugal compression force of an impeller by passing the gas throughthe impeller that is rotating. A diffuser passage is connected with animpeller outlet to convert kinetic energy into pressure energy of gas bydecelerating high-speed and high-pressure gas discharged from theimpeller while reducing noise and improving blowing efficiency.

When a flow rate of gas that passes through the impeller is reduced or apressure difference between an inlet and an outlet of the impellerdecreases, an air current becomes instable. Therefore, a counter currentis generated in the diffuser passage, and as a result, stall and surgephenomena appear. Moreover, when the flow rate of gas is further reducedor the pressures at the inlet and the outlet of the impeller are thesame as each other, a surge mode in which a complete counter current isperiodically generated in the diffuser passage starts to therebysignificantly deteriorate compressor efficiency.

Therefore, there was presented a variable diffuser that can vary an areaof the diffuser passage so as to minimize the stall and the surge andcontrol the flow rate. A general variable diffuser is constituted by aplurality of veins placed in a circumferential direction of the diffuserpassage. In the variable diffuser, the area of the diffuser passage isreduced as the flow rate is reduced or the pressure difference betweenthe inlet and the outlet of the impeller decreases, and in the reversecase, the area of the diffuser passage is extended so as to stabilizethe air current.

However, the impeller outlet cannot be fully sealed with the variablediffuser in the related art and gas flows backwards through a spacebetween the impeller and the variable diffuser. Therefore, there is alimit in preventing the stall and the surge. Further, the variablediffuser in the related art is limited in a flow rate control range anda maximum flow rate range which can be controlled with the variablediffuser in the related art is approximately 45% of a rated flow rate.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide a gascompressor and a method for controlling a flow rate of the gascompressor that can effectively prevent stall and surge by preventinggas from flowing backwards by modifying a variable diffuser system.

Further, the present invention has been made in an effort to provide agas compressor and a method for controlling a flow rate of the gascompressor that can extend a maximum flow rate range which can becontrolled by modifying a variable diffuser system.

An exemplary embodiment of the present invention provides a gascompressor including: i) an impeller fixed to a rotation shaft andhaving a plurality of blades each including a wing surface and an edgesurface on an outer circumferential surface thereof; ii) a shroudsurrounding the wing surface and having an outer wall parallel to theedge surface; and iii) a ring valve installed on a diffuser passageconnected with an outlet of the impeller to open and close the diffuserpassage and maintaining a gap from the end of the impeller in a radialdirection of the impeller. The ring valve slidably moves on the outerwall of the shroud while contacting the outer wall of the shroud.

The ring valve may maintain a gap G of a condition described below fromthe end of the impeller in the radial direction of the impeller,

0.002D≦G≦0.0080D

wherein, D represents a diameter (mm) at the outlet of the impeller.

The gas compressor may further include a plurality of veins installed ina circumferential direction of the diffuser passage outside the ringvalve in the diffuser passage.

Another exemplary embodiment of the present invention provides a gascompressor including: i) an impeller fixed to a rotation shaft andhaving a plurality of blades each including a wing surface and an edgesurface on an outer circumferential surface thereof; ii) a shroudsurrounding the wing surface; iii) a ring valve installed on a diffuserpassage connected with an outlet of the impeller and moving in adirection parallel to the rotation shaft to open and close the diffuserpassage; iv) a plurality of veins installed in a circumferentialdirection of the diffuser passage outside the ring valve in the diffuserpassage and each having a vein shaft; and v) an actuator coupled withthe ring valve and the plurality of vein shafts to sequentially controlmovement of the ring valve and rotational angles of the veins.

The ring valve may maintain a gap G of a condition described below fromthe end of the impeller in the radial direction of the impeller,

0.002D≦G≦0.0080D

wherein, D represents a diameter (mm) at the outlet of the impeller. Anouter wall of the shroud may be parallel to the edge surface and thering valve may slidably move on the outer wall of the shroud whilecontacting the outer wall of the shroud.

In the impeller, spaces among the blades may be in communication witheach other over the wing surface inside the shroud. On the contrary, inthe impeller, the spaces among the blades may be separated from eachother by a cover plate on the wing surface.

The actuator may include: i) an inner guide ring surrounding the veinshaft; ii) a plurality of ball levers penetrating the inner guide ringand the vein shaft in the radial direction of the impeller to couple theinner guide ring and the vein shaft with each other; iii) an outer guidering surrounding the inner guide ring, integrally connected with thering valve by a connector, and having a slant sliding hole; and iv) afixing pin fixed to the inner guide ring through the slant sliding hole.The gas compressor may further include a diffuser frame supporting thevein shaft, the inner guide ring, and the ring valve.

The vein shaft may have a cavity penetrating the vein shaft in theradial direction of the impeller and the inner guide ring may have aplurality of openings facing the cavity in the radial direction of theimpeller. Each of the plurality of ball levers may include a ball memberclosely attached to a side wall of the opening of the inner guide ringand a support member inserted to the cavity to be fixed to the veinshaft.

The actuator may further include: i) a stop member controlling arotational speed of the inner guide ring; ii) a control handle fixed tothe outer guide ring; and iii) an elastic member installed between thediffuser frame and the fixing pin.

The stop member may include; a pair of first bars positioned with adistance in the circumferential direction on one surface of the innerguide ring; and a second bar fixed to the diffuser frame and protrudingso that a part thereof is positioned between the pair of first bars.

On the contrary, the actuator may include: i) a link member fixed to thevein shaft; ii) a guide shaft fixed to the link member with a distancefrom the vein shaft; and iii) a control member rotating the vein shaftby moving the guide shaft while forming a first guide groove receivingthe guide shaft on one surface thereof.

The first guide groove may be formed in the radial direction of theimpeller, and the control member may further include a second guidegroove formed in a circumferential direction of the control member whilebeing linked with the first guide groove. The gas compressor may furtherinclude a diffuser frame supporting the ring valve, and the vein shaftand the control member while surrounding the ring valve, and in thediffuser frame, the slant sliding hole may be formed in a regionoverlapping with the ring valve.

The control member may further include a third guide groove formed on aninner surface of the control member while being linked with the secondguide groove. The actuator may further include a fixing key of which oneend is fixed to the ring valve by penetrating the slant sliding hole andthe other end is received in the third guide groove.

In the diffuser frame, a plurality of vein holes which the vein shaftpenetrates may be formed in a direction parallel to the rotation shaftand the slant sliding hole may be spaced apart from the vein holebetween two adjacent vein holes. The control member may be connectedwith a control unit sensing an operational condition of the gascompressor to be operated by a command from the control unit.

On the contrary, the actuator may include: i) a first actuator coupledwith the plurality of vein shafts to control the rotational angles ofthe veins; and ii) a second actuator coupled with the ring valve tocontrol the movement of the ring valve. The first actuator may include:i) a link member fixed to the vein shaft; ii) a guide shaft fixed to thelink member with a distance from the vein shaft; and iii) a controlmember rotating the vein shaft by moving the guide shaft while forming afirst guide groove receiving the guide shaft on one surface thereof.

The first guide groove may be formed in the radial direction of theimpeller, and the control member may further include a second guidegroove formed in a circumferential direction of the control member whilebeing linked with the first guide groove.

The ring valve may have an extension ring on an outer surface thereof,and the actuator may include: i) a first nozzle spraying compressed airto one surface of the extension ring toward the diffuser passage; andii) a second nozzle spraying compressed air to one opposite surface ofthe extension ring which is faraway from the diffuser passage.

The gas compressor may further include a top cover installed between thediffuser frame and the ring valve. The first nozzle may be formedthroughout the top cover and the diffuser frame and the second nozzle isformed on the top cover. The control member, and the first and secondnozzles may be connected with the control unit sensing the operationalcondition of the gas compressor to be operated by the command from thecontrol unit.

Yet another exemplary embodiment of the present invention provides amethod for controlling a flow rate of a gas compressor, including; i)sealing a diffuser passage by closing a ring valve in initial operationand reducing an area of the diffuser passage outside the ring valve byclosing a plurality of veins; ii) opening the diffuser passage byopening the ring valve for rated operation; and iii) increasing the areaof the diffuser passage outside the ring valve by opening the pluralityof veins.

The method may further include; for stopping the operation after theincreasing of the area of the diffuser passage, i) reducing the area ofthe diffuser passage outside the ring valve by closing the plurality ofveins; and ii) sealing the diffuser passage by closing the ring valve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a gas compressor accordingto a first exemplary embodiment of the present invention.

FIG. 2 is a partially enlarged diagram of the gas compressor shown in

FIG. 1.

FIG. 3 is a plan view schematically showing an impeller and a ring valvein the gas compressor shown in FIG. 1.

FIG. 4 is a plan view schematically showing an impeller and a ring valvein a gas compressor according to a comparative example.

FIG. 5 is a graph showing measurement of a vibration state depending onvariation of a gap between a ring valve and the end of an impeller.

FIGS. 6 and 7 are exploded perspective views of a variable diffusersystem in the gas compressor shown in FIG. 1.

FIG. 8 is a cross-sectional view of an outer guide ring, a ring valve,and a connector in the variable diffuser system shown in FIG. 7.

FIG. 9 is a perspective view of a combined state of the variablediffuser system in the gas compressor shown in FIG. 1.

FIGS. 10 to 13 are schematic diagrams of a variable diffuser systemshown to describe a method for controlling a flow rate in the gascompressor according to the first exemplary embodiment of the presentinvention.

FIG. 14 is a partial cross-sectional view of a gas compressor accordingto a second exemplary embodiment of the present invention.

FIG. 15 is a partially enlarged diagram of the gas compressor shown inFIG. 14.

FIG. 16 is an exploded perspective view of a variable diffuser system inthe gas compressor shown in FIG. 14.

FIG. 17 is a partially enlarged diagram of FIG. 16.

FIG. 18 is a perspective view showing a combined state of a diffuserframe and a ring valve shown in FIG. 17.

FIG. 19 is a right side view of the variable diffuser system in the gascompressor shown in FIG. 14.

FIG. 20 is a partially enlarged perspective view showing a part of acontrol member, and a guide shaft and a fixation key in a configurationof the variable diffuser system shown in FIG. 19.

FIGS. 21 to 23 are perspective views showing states of a ring valve anda vein at points (a), (b), and (c) shown in FIG. 19, respectively.

FIG. 24 is a partial cross-sectional view of a gas compressor accordingto a third exemplary embodiment of the present invention.

FIG. 25 is an exploded perspective view of a variable diffuser system inthe gas compressor shown in FIG. 24.

FIG. 26 is a right side view of the variable diffuser system shown inFIG. 24.

FIG. 27 is a partially enlarged diagram of the gas compressor shown inFIG. 24.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. As those skilled in the art would realize,the described embodiments may be modified in various different ways, allwithout departing from the spirit or scope of the present invention.

FIG. 1 is a partial cross-sectional view of a gas compressor 100according to a first exemplary embodiment of the present invention.

Referring to FIG. 1, the gas compressor 100 of the first exemplaryembodiment includes a rotation shaft 11, an impeller 12, a shroud 13, aring valve 14, a plurality of veins 15 (one vein is shown in FIG. 1),and an actuator 20. The gas compressor 100 shown in FIG. 1 has bilateralsymmetry around a center line (A-A line) of the rotation shaft 11.

The impeller 12 is fixed to the rotation shaft 11 and the rotation shaft11 is coupled to a rotation shaft of a motor (not shown). A plurality ofblades 16 having a curved radial pattern are formed on an externalcircumferential surface of the impeller 12. The blade 16 includes a wingsurface 161 formed at a predetermined curvature and an edge surface 162connected to the wing surface 161 and parallel to the rotation shaft 11.The shroud 13 is installed to surround the impeller 12 at apredetermined gap from the wing surface 161 of the blade 16.

When a motor operates to rotate the impeller 12, external gas flows intothe rotating impeller 12 and is accelerated and compressed while passingthrough spaces among the blades 16 and thereafter, the external gas isdischarged outside the edge surfaces 162 of the blades 16. In FIG. 1, aflow-in direction and a discharge direction of gas are indicated byarrows. In the exemplary embodiment, an outlet of the impellerrepresents a vicinity of the end of the impeller 12 where the compressedgas is discharged.

A diffuser passage 17 is positioned outside the outlet of the impeller12. The diffuser passage 17 as a space formed between a discharge scroll18 and a diffuser frame 30 is provided to have a ring shape having apredetermined height and a predetermined width. The diffuser passage 17is connected with an internal passage of the discharge scroll 18 andconverts kinetic energy into pressure energy of gas by diffusing anddecelerating the high-speed and high-pressure gas discharged from theimpeller 12.

In the exemplary embodiment, the ring valve 14, the plurality of veins15, and the actuator 20 constitute a variable diffuser system. The ringvalve 14 operates to open and close the diffuser passage 17 and preventsstall and surge by sealing the diffuser passage 17 at initial operation.The plurality of veins 15 operate to vary a rotational angle andstabilizes an air current by varying an area of the diffuser passage 17outside the ring valve 14. The actuator 20 is mechanically coupled withthe ring valve 14 and the plurality of veins 15 to sequentially controlthe movement of the ring valve 14 and the rotational angle of the vein15.

FIG. 2 is a partially enlarged diagram of the gas compressor 100 shownin FIG. 1 and shows a state in which the ring valve 14 descends towardthe discharge scroll 18 to seal the diffuser passage 17. FIG. 3 is aplan view schematically showing the impeller 12 and the ring valve 14 inthe gas compressor 100 shown in FIG. 1.

Referring to FIGS. 2 and 3, an outer wall 131 of the shroud 13 isparallel to the edge surface 162 of the blade 16 and maintains apredetermined gap from the edge surface 162 and the end of the impeller12 in a radial direction of the impeller 12. Herein, the ‘radialdirection’ represents a direction rambling over in a directionperpendicular to the rotation shaft 11 from the center of the impeller12.

The ring valve 14 contacts the outer wall of the shroud 13 and slides onthe outer wall 131 of the shroud 13 to open or close the diffuserpassage 17. Therefore, when the ring valve 14 descends toward thedischarge scroll 18 to seal the diffuser passage 17, the ring valve 14maintains the predetermined gap from the edge surface 162 and the end ofthe impeller 12.

In the exemplary embodiment, the gap G (see an enlarged circle of FIG.2, and FIG. 3) between the ring valve 14 and the end of the impeller 12measured in the radial direction of the impeller 12 is set to meet thefollowing condition according to a diameter D (mm) (see FIG. 3) at theoutlet of the impeller 12.

0.002D≦G≦0.0080D  (1)

A minimum value of the gap G is set by considering limitations such asthermal expansion of the impeller 12 and the ring valve 14 and a radialclearance of the rotation shaft 11. That is, when the gap G is less than0.002 D, the impeller 12 and the ring valve 14 may contact each other bythe thermal expansion of the impeller 12 and the ring valve 14 and it isdifficult to precisely adjust the clearance between the rotation shaft11 and the impeller 12 during installation. Further, when assemblyprecision is low, the impeller 12 may hit the ring valve 14 while thegas compressor 100 operates.

A maximum value of the gap G is set by considering functionality of thering valve 14 preventing the stall and the surge. That is, when the gapG is more than 0.008 D, gas flows backwards through a space between theimpeller 12 and the ring valve 14 to cause the stall and the surge, andas a result, stability and efficiency of the gas compressor 100deteriorates significantly. The gas compressor 100 of the firstexemplary embodiment may implement high efficiency as the gap G betweenthe ring valve 14 and the end of the impeller 12 is set to be closer tothe minimum value in the range of Condition (1).

The diameter D at the outlet of the impeller 12 may be in the range of10 to 800 mm and in this case, the gap G between the ring valve 14 andthe end of the impeller 12 may be set to the range of 0.02 to 6.4 mmaccording to Condition (1). When the gas compressor 100 is a high-speedgas compressor of 7,000 rpm or more, although the gap G may varydepending on rated air volume and pressure, the gap G may be 0.2 mm ifthe diameter D at the outlet of the impeller 12 is 50 mm and the gap Gmay be 2 mm if the diameter D at the outlet of the impeller 12 is 500mm.

FIG. 4 is a plan view schematically showing an impeller 12 and a ringvalve 14′ in a gas compressor according to a comparative example inwhich a gap G2 between the ring valve 14′ and the end of the impeller 12is more than 0.008 D. Referring to FIGS. 3 and 4, the reason why adifference in stability and efficiency is generated between the gascompressor of the exemplary embodiment that meets Condition (1) and thegas compressor of the comparative example that does not meet Condition(1) will be described. In FIGS. 3 and 4, arrow B represents a rotationaldirection of the impeller 12.

First, referring to FIG. 3, in the gas compressor 100 of the exemplaryembodiment, the ring valve 14 maintains the gap G that meets Condition(1) from the end of the impeller 12 on the circumference of the impeller12. For example, when the diameter D at the outlet of the impeller 12 is200 mm, the gap G is set to the range of 0.4 to 1.6 mm.

In the gas compressor 100 of the exemplary embodiment, when the ringvalve 14 descends to seal the diffuser passage 17, the impeller 12 iscompletely surrounded by the shroud 13 and the ring valve 14 except foran inlet into which external gas flows. When initial operation starts inthis state, gas compressed in spaces 19 among the blades 16 cannot bedischarged outside the impeller 12 and just continuously rotates in thesame space while the gas cannot flow backwards against the impeller 12due to centrifugal force.

In FIG. 3, a rotational direction of the compressed gas is indicated bya dotted arrow. Therefore, the entirety of the spaces 19 among theblades 16 is filled with the compressed gas and external gas cannot besuctioned at the inlet of the impeller 12 any more.

As a result, while gas is not additionally suctioned other than aminimum amount of gas suctioned at initial operation, since a rotationspeed of the gas compressor increases up to a rated rotation speed,no-load operation can be implemented and the stall and surge caused dueto the backflow of gas can be prevented. Further, even in the case wheregas flows backwards to the impeller 12 due to a problem in a used placeconnected with the discharge scroll 18, the backflow of gas can beprevented by sealing the diffuser passage 17 with the ring valve 14,thereby effectively suppressing the stall and the surge.

Referring to FIG. 4, in the gas compressor of the comparative example,the ring valve 14′ maintains the gap G2 that does not meet Condition (1)from the end of the impeller 12 on the circumference of the impeller 12.For example, when the diameter D at the outlet of the impeller 12 is 200mm, the gap G2 is more than 1.6 mm.

In the case of the comparative example, gas flows backwards through aspace between the impeller 12 and the ring valve 14′. That is,compressed gas in the spaces 19 among the blades 16 when the impeller 12rotates flows backwards to spaces among other blades in a directionopposite to a rotation direction of the impeller 12 through a spacebetween the impeller 12 and the ring valve 14′ to flows toward the inletof the impeller 12. In FIG. 4, a flow direction of the compressed gas isindicated by an arrow. Therefore, in the gas compressor of thecomparative example, no-load operation cannot be implemented, and thestall and surge caused due to the backflow of gas are permitted.

FIG. 5 is a graph showing measurement of a vibration state depending onvariation of a gap G between a ring valve and the end of an impeller. Inthe gas compressor used in an experiment, the diameter D at the outletof the impeller is 200 mm, the height of the blade is 18 mm, and theexperiment is performed under room temperature and atmospheric pressureconditions. The gap G between the ring valve and the end of the impelleris 0.4 mm or more according to Condition (1) and a vibration value ofthe impeller is measured while extending the gap by each 0.2 mm.

Referring to FIG. 5, as the gap G between the ring valve and the end ofthe impeller increases, the vibration value gradually increases, but arange in which the gap G is equal to or less than 1.6 mm belongs to anormal operation range. On the contrary, it can be verified that thevibration value increase rapidly while the gap G is more than 1.6 mm toenter an initial stall and surge region. From the result of FIG. 5,stability and efficiency are significantly deteriorated in the gascompressor of the comparative example that does not meet Condition 1.

In the gas compressor 100 of the first exemplary embodiment, the ringvalve 14 basically has a flow rate control function and more primarilyserves as a valve that closes the entire outlet of the impeller 12 sothat the compressed gas cannot deviate from the impeller 12. Therefore,the backflow of gas is prevented by using the ring valve 14 toeffectively prevent the stall and the surge.

The actuator 20 is mechanically coupled with the ring valve 14 and theplurality of veins 15 and sequentially control the movement of the ringvalve 14 and the rotational angle of the vein 15. Next, a couplingstructure of the ring valve 14, the plurality of veins 15, and theactuator 20 will be described.

FIGS. 6 and 7 are exploded perspective views of a variable diffusersystem in the gas compressor 100 shown in FIG. 1.

Referring to FIGS. 6 and 7, the plurality of veins 15 are arranged atregular intervals in a circumferential direction of the diffuser passage17 at one portion of the diffuser frame 30. A vein shaft 21 is fixed toeach vein 15 and a cavity 211 penetrating the vein shaft 21 is formed onthe vein shaft 21 in a radial direction.

The diffuser frame 30 includes a first flange 31 and a second flangethat are spaced apart from each other, and a connection flange 33connecting an inner end of the second flange 32 with an inner end of thefirst flange 31. A plurality of first openings 301 for mounting the veinshaft 21 are arranged in the first and second flanges 31 and 32 atregular intervals in a circumferential direction.

The actuator 20 includes an inner guide ring 22 surrounding theplurality of vein shafts 21, a plurality of ball levers 23 coupling theinner guide ring 22 with the vein shafts 21, an outer guide ring 24integrally connected with the ring valve 14 while surrounding the innerguide ring 22, and a plurality of fixing pins 25 coupling the outerguide ring 24 with the inner guide ring 22.

A plurality of second openings 221 penetrating the inner guide ring 22in the radial direction of the impeller 12 are arranged in the innerguide ring 22 at regular intervals in the circumferential direction.When the vein shaft 21 penetrates the first openings 301 of the diffuserframe 30 to be coupled to the diffuser frame 30, the inner guide ring 22is placed outside the connection flange 33 and the second flange 32 tosurround the plurality of vein shafts 21. In this case, the cavity 211of the vein shaft 21 and the second openings 221 of the inner guide ring22 are placed to face each other in the radial direction.

The ball lever 23 penetrates the second openings 221 of the inner guidering 22 and the cavity 211 of the vein shaft 21 to be fixed to the veinshaft 21. The ball lever 23 includes a ball member 231 closely attachedto a side wall of the second opening 221 of the inner guide ring 22 anda support member 232 inserted into the cavity 211 to be fixed to thevein shaft 21. Therefore, when the inner guide ring 22 rotates, the veinshaft 21 rotates together in link with the inner guide ring 22 throughthe ball lever 23.

A stop member 26 controlling a rotational speed of the inner guide ring22 is installed in the diffuser frame 30 and the inner guide ring 22.The stop member 26 includes a pair of first bars 27 positioned on onesurface of the inner guide ring 22 with a distance from each other inthe circumferential direction and a second bar 28 fixed to the diffuserframe 30 and protruding so that a portion thereof is positioned betweenthe pair of first bars 27. The pair of first bars 27 are positionedspaced apart from each other by a maximum rotational distance of theinner guide ring 22 and the rotation of the inner guide ring 22 islimited while any one of the pair of first bars 27 is suspended to thesecond bar 28.

Meanwhile, an inner space into which a fixing screw 29 is inserted isformed in the vein shaft 21 to strongly fasten the ball lever 23 withthe fixing screw 29. Further, a plurality of third openings 331penetrating the connection flange 33 in the radial direction of theimpeller 12 are formed in the connection flange 33. At the time ofdisassembling the variable diffuser system, the ball lever 23 is pushedout by pushing a tool into the third opening 331 from the inside of theconnection flange 33 to thereby separate the ball lever 23 from the veinshaft 21.

The outer guide ring 24 is positioned in parallel to the ring valve 14and is formed integrally with the ring valve 14 by a connector 34. FIG.8 is a cross-sectional view of the outer guide ring 24, the ring valve14, and the connector 34 in the variable diffuser system shown in FIG.7. Referring to FIG. 8, the outer guide ring 24 is lower than the ringvalve 14 and the connector 34 integrally connects the end of the ringvalve 14 and the end of the outer guide ring 24.

Referring back to FIGS. 6 and 7, one or more slant sliding holes 35 areformed in the outer guide ring 24. As one example, four slant slidingholes 35 may be arranged in the circumferential direction of the outerguide ring 24. The fixing pins 25 are provided as many as the slantsliding holes 35 and each of the fixing pins 25 is fixed to the innerguide ring 22 through the slant sliding hole 35.

FIG. 9 is a perspective view of a combined state of the variablediffuser system in the gas compressor 100 shown in FIG. 1.

Referring to FIG. 9, an elastic member 36 is installed between thediffuser frame 30 and the fixing pin 25. One end of the elastic member36 is fixed to the diffuser frame 30 and the opposite end of the elasticmember 36 is fixed to the fixing pin 25. The elastic member 36 exertsforce to pull the fixing pin 25 in a clockwise direction (based on thefigure) by using restoration force.

In addition, a control handle 37 is attached to the outer guide ring 24to control the rotation of the outer guide ring 24 by operating thecontrol handle 37. The control handle 37 is connected with a controlunit 38 that senses operational conditions of the gas compressor 100such as a flow rate of gas passing through the impeller 12, a differencein pressure between the inlet and the outlet of the impeller 12, thebackflow of gas caused due to a problem in a used place, and is operatedby a command from the control unit 38.

Referring to FIGS. 9 to 13, a method for controlling the flow rate ofthe gas compressor 100 using the variable diffuser system will bedescribed. A ‘clockwise direction’ and a ‘counterclockwise direction’ tobe described below are based on the figures.

FIGS. 10 and 11 show states of the ring valve 14 and the vein 15 forinitial operation. Referring to FIGS. 10 and 11, the outer guide ring 24and the ring valve 14 descend in the initial operation, such that thering valve 14 seals the diffuser passage 17. In addition, the pluralityof veins 15 maintain a closed state to minimize an area of the diffuserpassage 17 outside the ring valve 14 (step S1).

In this case, a fixing pin 25 is positioned at an upper end of a slantsliding hole 35. In addition, an elastic member 36 pulls the fixing pin25 in the clockwise direction by using restoration force, but the innerguide ring 22 cannot be moved in the clockwise direction any longer bythe stop member 26. Therefore, an angle of the vein 15 is limited at adesigned minimum flow rate position.

As described above, when the operation of the gas compressor 100 startswith the diffuser passage 17 sealed with the ring valve 14, no-loadoperation can be implemented as described above with reference to FIG.3. Further, the stall and the surge can be suppressed by preventing thebackflow of the compressed gas.

Thereafter, the control handle 37 and the outer guide ring 24 arerotated in the counterclockwise direction for rated operation.Therefore, as shown in FIG. 9, the fixing pin 25 serves as a slantguide, such that the outer guide ring 24 ascends from the diffuser frame30. Therefore, the ring valve 14 ascends to open the diffuser passage 17(step S2).

In this case, since the elastic member 36 pulls the fixing pin 25 in theclockwise direction, the inner guide ring 22 and the vein 15 linkedtherewith maintain the minimum flow rate position without moving. Instep S2, the fixing pin 25 is positioned at a lower end of the slantsliding hole 35.

Thereafter, the control handle 37 and the outer guide ring 24 arefurther rotated in the counterclockwise direction. Therefore, as shownin FIGS. 12 and 13, the outer guide ring 24 overcomes the restorationforce of the elastic member 36 applied to the fixing pin 25 withoutvariation in height, and pulls and rotates the fixing pin 25 in thecounterclockwise direction. As a result, the vein 15 is opened while thefixing pin 25, and the inner guide ring 22 and the vein shaft 21 move toincrease an area of the diffuser passage 17 (step S3). During thisprocess, the fixing pin 25 moves until the rotation of the inner guidering 22 is stopped by the stop member 26.

Next, an operational sequence for the stop is opposite to theabove-mentioned process.

That is, in FIG. 12, when the control handle 37 rotates in the clockwisedirection, the elastic member 36 pulls the fixing pin 25 in theclockwise direction, such that the fixing pin 25 cannot serve as theslant guide with respect to the outer guide ring 24. Therefore, theouter guide ring 24 may just rotate in the clockwise direction withoutvariation in height and the fixing pin 25 pulled by the restorationforce of the elastic member 36 moves in the clockwise direction to closethe vein 15 (step S4, see FIG. 9). During this process, the fixing pin25 moves until the rotation of the inner guide ring 22 is stopped by thestop member 26.

In addition, in FIG. 9, when the control handle 37 is further rotated inthe clockwise direction, the fixing pin 25 serves as the slant guide,and as a result, the outer guide ring 24 and the ring valve 14 descendto seal the diffuser passage 17 as shown in FIG. 11 (step S5).Therefore, even for a period from the rated operation to the stopping ofthe impeller 12, the surge can be effectively suppressed.

As described above, in the gas compressor 100 of the exemplaryembodiment, since the ring valve 14 and the plurality of veins 15 aretogether controlled by using a single actuator 20, a mechanicalconfiguration for the control can be simplified. Further, in the gascompressor 100 of the exemplary embodiment, since the ring valve 14 andthe vein 15 are sequentially driven, a flow rate range which can becontrolled with the variable diffuser system may be extended to themaximum 100%. In the exemplary embodiment, a flow rate control range ofthe ring valve 14 is approximately in the range of 0 to 45% and a flowrate control range of the vein 15 is approximately in the range of 45 to100%.

Meanwhile, in FIGS. 1 to 3, a structure in which spaces among blades 16can be in communication with each other over a wing surface 161 inside ashroud 13 is shown, but a structure in which a cover plate (not shown)is fixed to the wing surface 161 to separate the spaces among the blades16 from each other on the wing surface 161 can also be applied.

That is, in the case of the latter, the spaces among the blades 16 areseparated by the cover plate except for an inlet of the impeller 12 intowhich gas flows and an outlet (an edge surface) through which compressedgas is discharged. The cover plate rotates together with the impeller 12and maintains a distance from the shroud 13 inside the shroud 13. In thecase of the latter, the shape of the gas compressor 100 is the same asthe structure of the above-mentioned exemplary embodiment except for thecover plate and a gap G between the ring valve 14 and the end of theimpeller 12 also meet Condition (1) described above.

FIG. 14 is a partial cross-sectional view of a gas compressor 200according to a second exemplary embodiment of the present invention andFIG. 15 is a partially enlarged diagram of the gas compressor 200 shownin FIG. 14 and shows a state in which a ring valve 141 descends toward adischarge scroll 18 to seal a diffuser passage 17.

Referring to FIGS. 14 and 15, the gas compressor 200 of the secondexemplary embodiment includes a rotation shaft 11, an impeller 12, ashroud 132, a ring valve 141, a plurality of veins 15 (one vein is shownin FIG. 14), and an actuator 40.

The gas compressor 200 of the second exemplary embodiment has the sameconfiguration as the gas compressor 100 of the first exemplaryembodiment except for the shapes of the ring valve 141, and the actuator40 and the diffuser frame 50. The same reference numerals refer to thesame members as the first exemplary embodiment and members differentfrom the first exemplary embodiment will be primarily described below.

FIG. 16 is an exploded perspective view of a variable diffuser system inthe gas compressor 200 shown in FIG. 14 and FIG. 17 is a partiallyenlarged diagram of FIG. 16.

Referring to FIGS. 16 and 17, the plurality of veins 15 are arranged atregular intervals in a circumferential direction of the diffuser passage17 at one portion of the diffuser frame 50 and a vein shaft 21 is fixedto each vein 15.

The diffuser frame 50 includes a ring-shaped flange 51 and a cylindricalsupport portion 52 extending from the inside of the flange 51 with apredetermined height. The flange 51 is placed to face the dischargescroll 18 inside the shroud 132 to form the diffuser passage 17 betweenthe flange 51 and the discharge scroll 18. The support portion 52extends in a direction farther from the discharge scroll 18 from theinside of the flange 51.

A plurality of vein holes 53 penetrating the support portion 52 in adirection parallel to the rotation shaft 11 are formed in the supportportion 52. In addition, each vein shaft 21 is inserted into the veinhole 53, such that the vein 15 and the vein shaft 21 are supported bythe diffuser frame 50. In this case, the length of the vein shaft 21 islarger than the height of the support portion 52 and after the veinshaft 21 is coupled to the diffuser frame 50, the end of the vein shaft21 protrudes outside the support portion 52.

The end of the vein shaft 21 is fixed to one end of a link member 41 anda guide shaft 42 is fixed to one opposite end of the link member 41 witha predetermined distance from the vein shaft 21. The link member 41 andthe guide shaft 42 are provided as many as the vein shafts 21 and theguide shaft 42 is shorter than the vein shaft 21. As the vein shaft 21is connected with the guide shaft 42 through the link member 41, whenthe guide shaft 42 rotatably moves around the vein shaft 21, the veinshaft 21 rotates to control opening and closing degrees of the vein 15.

The ring valve 141 is coupled to the inside of the support portion 52and an outer surface of the ring valve 141 is closely attached to aninner surface of the support portion 52. A plurality of slant slidingholes 54 penetrating the support portion 52 in the radial direction ofthe impeller 12 are formed in the support portion 52. The slant slidinghole 54 is positioned between two adjacent vein holes 53 not to beconnected with the vein hole 53 and placed to be slant in a directionparallel to the rotation shaft 11.

FIG. 18 is a perspective view showing a combined state of the diffuserframe 50 and the ring valve 141 shown in FIG. 17.

Referring to FIG. 18, after the ring valve 141 is coupled to the insideof the support portion 52, a plurality of fixing keys 55 penetrate theslant sliding holes 54 outside the support portion 52 and thereafter,are fixed to the ring valve 141. In this case, the end of the fixing key55 protrudes outside the support portion 52. In addition, the width ofthe fixing key 55 is smaller than that of the slant sliding hole 54,such that the fixing key 55 moves in a longitudinal direction of theslant sliding hole 54.

When the fixing key 55 is positioned at the end of the slant slidinghole 54 which is faraway from the flange 51, the ring valve 141 ispositioned with a distance from the discharge scroll 18 to open thediffuser passage 17. On the contrary, when the fixing key 55 ispositioned at the end of the slant sliding hole 54 toward the flange 51,the ring valve 141 contacts the discharge scroll 18 to seal the diffuserpassage 17. The former is indicated by a solid line and the latter isindicated by dotted lines.

Referring back to FIGS. 16 and 17, a ring-shaped control member 43 isinstalled outside the support portion 52. The control member 43 iscoupled with the fixing key 55 to move the fixing key 55, therebycontrolling forward and backward movements of the ring valve 141. At thesame time, the control member 43 is coupled with even the guide shaft 42to rotatably move the guide shaft 42, thereby controlling a rotationalangle of the vein 15. In the gas compressor 200 of the second exemplaryembodiment, the control member 43, the plurality of link members 41, theplurality of guide shafts 42, and the plurality of fixing keys 55constitute the actuator 40.

A plurality of guide grooves 433 are formed on one surface of thecontrol member 43 in the radial direction. In addition, second guidegrooves 432 connected with the first guide grooves 431 are formed in acircumferential direction of the control member 43. The first and secondguide grooves 431 and 432 are provided as many as the vein shafts 21.Further, third guide grooves 433 are formed on an inner surface of thecontrol member 43 in a thickness direction of the control member 43. Thethird guide grooves 433 are provided as many as the fixing keys 55 andare finked with the second guide grooves 432.

The guide shaft 42 is received in the first and second guide grooves 431and 432 to move along the first and second guide grooves 431 and 432when the control member 43 rotates. The fixing key 55 is received in thethird guide groove 433 to move along the third guide groove 433 when thecontrol member 43 rotates. A control handle 37 transmitting rotatingpower to the control member 43 is positioned on an outer surface of thecontrol member 43. The control handle 37 is connected with the controlunit 38 to be operated by the command from the control unit 38.

FIG. 19 is a right side view of the variable diffuser system in the gascompressor 200 shown in FIG. 14 and FIG. 20 is a partially enlargedperspective view showing a part of the control member 43 and the guideshaft 42 and the fixing key 55 in a configuration of the variablediffuser system shown in FIG. 19.

Referring to FIGS. 19 and 20, the control member 43 sequentiallycontrols the position of the ring valve 141 and the rotational angle ofthe vein 15 depending on the rotational direction and the rotationalangle. That is, a movement amount of the ring valve 141 is controlledthrough the rotation of the control member 43 in a first section betweenpoint (a) and point (b). In addition, the rotational angle of the vein15 is controlled through the rotation of the control member 43 in asecond section between point (b) and point (c).

First, the fixing key 55 at point (a) is positioned at the end of theslant sliding hole 54 toward the discharge scroll 18 (see a dotted linemark of FIG. 18). Therefore, the ring valve 141 contacts the dischargescroll 18 to seal the diffuser passage 17. In this case, the end of thefixing key 55 is positioned at the end of the third guide groove 433toward the discharge scroll 18. Further, the guide shaft 42 at point (a)is positioned at the end of the second guide groove 432 which is farawayfrom the first guide groove 431. In this state, a slant angle of thevein 15 to a tangent line of the outer surface of the ring valve 141 isminimized to reduce an area of the diffuser passage 17.

When the control handle 37 moves toward point (b) from point (a) torotate the control member 43 in the counterclockwise direction, thefixing key 55 moves in a direction which is faraway from the dischargescroll 18 along the third guide groove 433. Therefore, the ring valve141 moves backwards to open the diffuser passage 17.

The position of the guide shaft 42 does not vary in a first section, butthe guide shaft 42 is positioned at the end of the second guide groove432 which is linked with the first guide groove 431 at point (b) due tothe rotation of the control member 43. Since the position of the guideshaft 42 does not vary in the first section, the vein 15 maintains theclosed state as it is. As described above, in the first section, themovement amount of the ring valve 14 can be controlled without variationin rotational angle of the vein 15.

When the control handle 37 moves toward point (c) from point (b) tofurther rotate the control member 43 in the counterclockwise direction,the guide shaft 42 slidably moves along the first guide groove 431 torotate the vein shaft 21. Therefore, the vein 15 rotates so that theslant angle of the vein 15 to the tangent line of the outer surface ofthe ring valve 141 is maximized, thereby increasing the area of thediffuser passage 17.

The position of the fixing key 55 does not vary in the second section,but the fixing key 55 is positioned at the end of the second guidegroove 432 which is linked with the first guide groove 431 at point (c)due to the rotation of the control member 43. Since the position of thefixing key 55 does not vary in the second section, the ring valve 141maintains the opened state as it is. As described above, in the secondsection, the rotational angle of the vein 15 can be controlled withoutthe movement of the ring valve 141.

Referring to FIGS. 21 to 23, a method for controlling the flow rateusing the variable diffuser system will be described.

FIG. 21 is a perspective view showing states of the ring valve 141 andthe vein 15 at point (a) shown in FIG. 19.

Referring to FIG. 21, in initial operation, the ring valve 141 ascendsfrom the diffuser frame 50 to seal the diffuser passage 17. In addition,the plurality of veins 15 maintain the closed state to reduce an area ofthe diffuser passage 17 outside the ring valve 141 (step S1). Asdescribed above, when the operation of the gas compressor 200 startswith the diffuser passage 17 sealed with the ring valve 141, no-loadoperation can be implemented. Further, stall and surge can be suppressedby preventing backflow of compressed gas.

FIG. 22 is a perspective view showing states of the ring valve 141 andthe vein 15 at point (b) shown in FIG. 19.

Referring to FIG. 22, when the control handle 37 and the control member43 are rotated in the counterclockwise direction (based on FIG. 19) forrated operation, the fixing key 55 moves backwards the ring valve 141while moving along the third guide groove 433 to open the diffuserpassage 17 at the position of the ring valve 141 (step S2). In thiscase, the plurality of veins 15 maintain an initial state as it is.

FIG. 23 is a perspective view showing states of the ring valve 141 andthe vein 15 at point (c) shown in FIG. 19.

Referring to FIG. 23, when the control handle 37 and the control member43 are further rotated in the counterclockwise direction (based on FIG.19), the guide shaft 42 rotates the vein shaft 21 while moving along thefirst guide groove 431. Therefore, the plurality of veins 15 moves tothe maximum flow rate position to open the diffuser passage 17 (stepS3).

The rated operation is performed in step S3 and the area of the diffuserpassage 17 is varied for stabilization of air current by controlling thevein 15 depending on an operational state sensed by the control unit 38.Further, when the backflow of gas toward the impeller, which is causeddue to a problem in a used place is sensed in the rated operation, thevariable diffuser system returns to an initial position shown in FIG. 11to seal the diffuser passage 17 with the ring valve 141, therebypreventing the surge.

An operational sequence for the stop is in reverse order to theabove-mentioned process.

When the control handle 37 and the control member 43 are rotated in theclockwise direction (based on FIG. 19), the area of the diffuser passage17 is reduced while the vein 15 is closed as shown in FIG. 22 (step S4).Thereafter, when the control handle 37 and the control member 43 arefurther rotated in the clockwise direction (based on FIG. 19), the ringvalve 141 ascends from the diffuser frame 50 to seal the diffuserpassage 17 as shown in FIG. 21 (step S5). Therefore, even for a periodfrom the rated operation to the stopping of the impeller 12, the surgecan be effectively suppressed.

FIG. 24 is a partial cross-sectional view of a gas compressor 300according to a third exemplary embodiment of the present invention.

Referring to FIG. 24, the gas compressor 300 of the third exemplaryembodiment has a configuration in which a plurality of veins 15 and aring valve 142 are controlled by different actuators unlike the secondexemplary embodiment. That is, the gas compressor 300 of the thirdexemplary embodiment includes a first actuator 60 coupled with the veinshaft 21 to control the rotational angle of the vein 15, and a secondactuator 70 controlling forward and backward movements of the ring valve142 by using compressed air.

Basic configurations and operations of the vein 15 and the ring valve142 are same as in the second exemplary embodiment except for thestructures of the first and second actuators 60 and 70. The samereference numerals refer to the same members as the second exemplaryembodiment and members different from the second exemplary embodimentwill be primarily described below.

FIG. 25 is an exploded perspective view of a variable diffuser system inthe gas compressor 300 shown in FIG. 24 and FIG. 26 is a right side viewof the variable diffuser system shown in FIG. 24.

Referring to FIGS. 25 and 26, the shapes of the vein 15 and the veinshaft 21 are the same as in the second exemplary embodiment. The shapeof a diffuser frame 56 is the same as in the second exemplary embodimentexcept that a slant sliding hole is not formed in the support portion 52but a first nozzle 71 to be described below is formed in the diffuserframe 56.

A plurality of first guide grooves 441 are formed on one surface of acontrol member 44 in a radial direction. After the vein shaft 21 iscoupled to the diffuser frame 56, the end thereof protrudes outside thesupport portion 52, and the end of the vein shaft 21 is fixed to one endof a link member 41. A guide shaft 42 is fixed to one opposite end ofthe link member 41 with a predetermined distance from the vein shaft 21.The guide shaft 42 is received in the first guide groove 441 and thelink member 41 is placed in parallel to the radial direction. A controlhandle 37 transmitting rotating power to the control member 44 ispositioned on an outer surface of the control member 44.

In the third exemplary embodiment, the plurality of link members 41, theplurality of guide shafts 42, and the control member 44 constitute thefirst actuator 60. When the control member 44 is rotated in theclockwise direction (based on FIG. 26), the area of the diffuser passage17 is increased by rotating the vein shaft 21 and the vein 15 in thesame direction while the guide shaft 42 rotates along the first guidegroove 441 in the clockwise direction. On the contrary, when the controlmember 44 is rotated in the counterclockwise direction (based on FIG.26), the area of the diffuser passage 17 is decreased by rotating thevein shaft 21 and the vein 15 in the same direction while the guideshaft 42 rotates along the first guide groove 441 in thecounterclockwise direction.

FIG. 27 is a partially enlarged diagram of the gas compressor 300 shownin FIG. 24 and shows a state in which the ring valve 142 moves forwardstoward the discharge scroll 18 to seal the diffuser passage 17.

Referring to FIGS. 25 and 27, an extension ring 143 is formed on anouter surface of the ring valve 142 and the outer surface of theextension ring 143 is coupled to the inside of the support portion 152to be closely attached to an inner surface of the support portion 52. Atop cover 45 is installed between the support portion 52 and the ringvalve 142 and the top cover 45 is fixed to the support portion 52through screw connection. The ring valve 142 maintains a gap G from theend of the impeller 12, which meets Condition (1) in the radialdirection of the impeller 12 at the outlet of the impeller 12 like thesecond exemplary embodiment.

The second actuator 70 includes a first nozzle 71 which is formed in thetop cover 45 and the support portion 52 and sprays compressed air towardone surface (a left side surface of the extension ring based on FIG. 27)of the extension ring 143 toward the diffuser passage 17, and a secondnozzle 72 which is formed on the top cover 45 and sprays compressed airtoward the other surface (a right side surface of the extension ringbased on FIG. 27) of the extension ring 143 which is faraway from thediffuser passage 17.

Therefore, when the first nozzle 71 is opened to spray the compressedair through the first nozzle 71, the extension ring 143 moves backwardsthe ring valve 142 by receiving force in a direction which is farawayfrom the discharge scroll 18 to open the diffuser passage 17. On thecontrary, when the second nozzle 72 is opened to spray the compressedair through the second nozzle 72, the extension ring 143 moves forwardsthe ring valve 142 by receiving force toward the discharge scroll 18 toseal the diffuser passage 17.

In the variable diffuser system of the third exemplary embodiment, thecontrol handle 37 of the first actuator 60 and the first and secondnozzles 71 and 72 of the second actuator 70 are connected with thecontrol unit 38 to operate sequentially according to the command fromthe control unit 38. The method for controlling the flow rate of the gascompressor 300 using the ring valve 142 and the plurality of veins 15 isthe same as in the second exemplary embodiment.

Meanwhile, in FIGS. 12 and 27, a structure in which the spaces among theblades 16 can be in communication with each other over the wing surface161 inside the shroud 132 is shown, but a structure in which a coverplate (not shown) is fixed to the wing surface 161 to separate thespaces among the blades 16 from each other on the wing surface 161 canalso be applied.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A gas compressor, comprising: an impeller fixed to a rotation shaftand having a plurality of blades each including a wing surface and anedge surface on an outer circumferential surface thereof; a shroudsurrounding the wing surface and having an outer wall parallel to theedge surface; and a ring valve installed on a diffuser passage connectedwith an outlet of the impeller to open and close the diffuser passageand maintaining a gap from the end of the impeller in a radial directionof the impeller, wherein the ring valve slidably moves on the outer wallof the shroud while contacting the outer wall of the shroud.
 2. The gascompressor of claim 1, wherein: the ring valve maintains a gap G of acondition described below from the end of the impeller in the radialdirection of the impeller,0.002D≦G≦0.0080D wherein, D represents a diameter (mm) at the outlet ofthe impeller.
 3. The gas compressor of claim 2, further comprising: aplurality of veins installed in a circumferential direction of thediffuser passage outside the ring valve in the diffuser passage.
 4. Agas compressor, comprising: an impeller fixed to a rotation shaft andhaving a plurality of blades each including a wing surface and an edgesurface on an outer circumferential surface thereof; a shroudsurrounding the wing surface; a ring valve installed on a diffuserpassage connected with an outlet of the impeller and moving in adirection parallel to the rotation shaft to open and close the diffuserpassage; a plurality of veins installed in a circumferential directionof the diffuser passage outside the ring valve in the diffuser passageand each having a vein shaft; and an actuator coupled with the ringvalve and the plurality of vein shafts to sequentially control movementof the ring valve and rotational angles of the veins.
 5. The gascompressor of claim 4, wherein: the ring valve maintains a gap G of acondition described below from the end of the impeller in the radialdirection of the impeller,0.002D≦G≦0.0080D wherein, D represents a diameter (mm) at the outlet ofthe impeller.
 6. The gas compressor of claim 5, wherein: an outer wallof the shroud is parallel to the edge surface and the ring valveslidably moves on the outer wall of the shroud while contacting theouter wall of the shroud.
 7. The gas compressor of claim 6, wherein: inthe impeller, spaces among the blades are in communication with eachother over the wing surface inside the shroud.
 8. The gas compressor ofclaim 6, wherein: in the impeller, the spaces among the blades areseparated from each other by a cover plate on the wing surface.
 9. Thegas compressor of claim 4, wherein: the actuator includes an inner guidering surrounding the vein shaft; a plurality of ball levers penetratingthe inner guide ring and the vein shaft in the radial direction of theimpeller to couple the inner guide ring and the vein shaft with eachother; an outer guide ring surrounding the inner guide ring, integrallyconnected with the ring valve by a connector, and having a slant slidinghole; and a fixing pin fixed to the inner guide ring through the slantsliding hole, wherein the gas compressor further includes a diffuserframe supporting the vein shaft, the inner guide ring, and the ringvalve.
 10. The gas compressor of claim 9, wherein: the vein shaft has acavity penetrating the vein shaft in the radial direction of theimpeller and the inner guide ring has a plurality of openings facing thecavity in the radial direction of the impeller.
 11. The gas compressorof claim 10, wherein: each of the plurality of ball levers includes aball member closely attached to a side wall of the opening of the innerguide ring and a support member inserted to the cavity to be fixed tothe vein shaft.
 12. The gas compressor of claim 9, wherein: the actuatorfurther includes a stop member controlling a rotational speed of theinner guide ring; a control handle fixed to the outer guide ring; and anelastic member installed between the diffuser frame and the fixing pin.13. The gas compressor of claim 12, wherein: the stop member includes apair of first bars positioned with a distance in the circumferentialdirection on one surface of the inner guide ring; and a second bar fixedto the diffuser frame and protruding so that a part thereof ispositioned between the pair of first bars.
 14. The gas compressor ofclaim 4, wherein: the actuator includes a link member fixed to the veinshaft; a guide shaft fixed to the link member with a distance from thevein shaft; and a control member rotating the vein shaft by moving theguide shaft while forming a first guide groove receiving the guide shafton one surface thereof.
 15. The gas compressor of claim 14, wherein: thefirst guide groove is formed in the radial direction of the impeller,and the control member further includes a second guide groove formed ina circumferential direction of the control member while being linkedwith the first guide groove.
 16. The gas compressor of claim 15, furthercomprising: a diffuser frame supporting the ring valve, and the veinshaft and the control member while surrounding the ring valve, whereinin the diffuser frame, the slant sliding hole is formed in a regionoverlapping with the ring valve.
 17. The gas compressor of claim 16,wherein: the control member further includes a third guide groove formedon an inner surface of the control member while being linked with thesecond guide groove, and the actuator further includes a fixing key ofwhich one end is fixed to the ring valve by penetrating the slantsliding hole and the other end is received in the third guide groove.18. The gas compressor of claim 16, wherein: in the diffuser frame, aplurality of vein holes which the vein shaft penetrates are formed in adirection parallel to the rotation shaft and the slant sliding hole isspaced apart from the vein hole between two adjacent vein holes.
 19. Thegas compressor of claim 14, wherein: the control member is connectedwith a control unit sensing an operational condition of the gascompressor to be operated by a command from the control unit.
 20. Thegas compressor of claim 4 wherein: the actuator includes a firstactuator coupled with the plurality of vein shafts to control therotational angles of the veins; and a second actuator coupled with thering valve to control the movement of the ring valve, and the firstactuator includes a link member fixed to the vein shaft; a guide shatfixed to the link member with a distance from the vein shaft; and acontrol member rotating the vein shaft by moving the guide shaft whileforming the first guide groove receiving the guide shaft on one surfacethereof.
 21. The gas compressor of claim 20, wherein: the first guide isformed in the radial direction of the impeller, and the control memberfurther includes a second guide groove formed in the circumferentialdirection of the control member while being linked with the first guidegroove.
 22. The gas compressor of claim 20, wherein: the ring valve hasan extension ring on an outer surface thereof, and the second actuatorincludes a first nozzle spraying compressed air to the one surface ofthe extension ring toward the diffuser passage; and a second nozzlespraying compressed air to one opposite surface of the extension ringwhich is faraway from the diffuser passage.
 23. The gas compressor ofclaim 22, further comprising: a top cover installed between the diffuserframe and the ring valve, wherein the first nozzle is formed throughoutthe top cover and the diffuser frame and the second nozzle is formed onthe top cover.
 24. The gas compressor of claim 22, wherein: the controlmember, and the first and second nozzles are connected with the controlunit sensing the operational condition of the gas compressor to beoperated by the command from the control unit.
 25. A method forcontrolling a flow rate of a gas compressor including a ring valveinstalled in a diffuser passage connected with an outlet of an impeller,a plurality of veins installed in a circumferential direction of thediffuser passage outside the ring valve, vein shafts fixed to theplurality of veins, respectively, and an actuator coupled with the ringvalve and the vein shaft, the method comprising: sealing the diffuserpassage by closing the ring valve in initial operation and reducing anarea of the diffuser passage outside the ring valve by closing theplurality of veins; opening the diffuser passage by opening the ringvalve for rated operation; and increasing the area of the diffuserpassage outside the ring valve by opening the plurality of veins. 26.The method of claim 25, further comprising: for stopping the operationafter the increasing of the area of the diffuser passage, reducing thearea of the diffuser passage outside the ring valve by closing theplurality of veins; and sealing the diffuser passage by closing the ringvalve.